This invention pertains to the field of spectrometry, and in particular to ion mobility spectrometry (IMS). In one aspect, the invention pertains to a method and apparatus for analyte detection and identification verification using spectrometry and, in particular, IMS.
The term xe2x80x9cion mobility spectrometryxe2x80x9d refers to the principles, practice and instrumentation for characterizing chemical substances through gas phase ion mobilities. In modern analytical IMS methods, ion mobilities are determined from ion velocities that are measured in a drift tube at ambient pressure (i.e., atmospheric pressure) with supporting electronics. Ion mobilities are characteristic of substances and can provide a means for detecting and identifying chemical compounds, or specific components of a sample. In practice, the sample is vaporized (if not already in a vapor state) and is then introduced into the reaction region of a drift tube where neutral molecules of the vapor undergo ionization. The resultant ions, i.e., product ions, are injected into the drift region for mobility analysis. Mobility is determined from the drift velocity attained by ions in a weak electric field. Although the mobility analysis described above occurs in a drift tube, other apparatuses can be utilized for mobility analyses. The term xe2x80x9cspectrometry analyzerxe2x80x9d is used herein to refer to a drift tube or other apparatus utilized for mobility analyses.
Ion velocities are inversely dependent on the effective collisional cross section of an ion and this makes IMS a type of molecular size analyzer. As the reactant ions and product ions are drawn towards and collide with the detector plate, current is registered and a signal is generated. The mobility spectrum represents the ion current intensity as a function of time. In instances where ions of several identities and different mobilities exist in the drift tube, ions can be separated through differences in mobilities. In order to provide greater separation between mobilities of different components in the sample, it is common to react the sample vapor with a reactant or reagent to alter the mobility of the molecules of interest to give greater separation between those molecules and other molecules which can exist in the sample.
In particular applications, molecules of interest are combined with chemicals to produce a much larger molecule having a much lower mobility in the drift tube. For example, RDX (cyclo-1,3,5-trimethylene-2,4,6-trinitramine) reacts particularly well with chloride to form a large molecule known as an adduct. The adduct, being of larger size, moves through the drift tube relatively slowly compared to other molecules which can exist in the sample and, therefore, the peak which identifies the RDX adduct is displayed later on a time log than are the peaks for RDX itself and other components. Reactions using reagents as described are particularly effective for those substances of interest which are polar in nature.
In summary, ion mobility spectrometry is comprised of, and governed by, two sequential processes. These are: A) gas phase ionization in air (or nitrogen) at atmospheric pressure through collisional charge exchange or ion-molecule reactions, and B) ion characterization using mobilities of gas phase ions in a weak electric field at ambient pressure (i.e., atmospheric pressure).
Ion mobility spectrometry has received a renewed interest in the last few years where only a decade ago the technique was regarded largely as a curiosity or an anachronistic technology within the ion-molecule chemistry and vapor sensing community. The resurgence of IMS instrumentation and technique is related to its intrinsic features of response (excellent detection limits) and to practical considerations (size, weight, and power advantages) when compared with well-established technologies such as mass spectrometry or gas chromatography/mass spectrometry.
While the use of IMS as a detection tool has experienced recent attention, elementary concepts in IMS are still relatively unrefined as compared to techniques such as mass spectrometry. For example, comprehensive models of response characteristics do not exist. Also, ion mobility spectrometry is an inherently low level resolution technique, and the low resolution of the ion mobility spectrometer can result in the overlapping of interferent peaks with the analyte peaks of interest. Specifically, an interferent peak can appear at the time when an analyte peak is expected, generating a false alarm as to the presence of the subject of interest.
One of the current uses for IMS is for the detection of contraband. FIG. 1 is an environmental view showing a typical IMS application in an airport security station which uses spectrometers of the prior art, but can also use a spectrometer containing the improvements of the present invention. In the example shown, the security officer xe2x80x9cPxe2x80x9d is checking for contraband which can be left on the outside of a handbag xe2x80x9cAxe2x80x9d. The security officer will wipe the outer surface of the bag xe2x80x9cAxe2x80x9d with a small paper wipe xe2x80x9cBxe2x80x9d. The paper wipe xe2x80x9cBxe2x80x9d is then inserted into a receptacle 11 in the ion mass spectrometer 1. Typically, air is drawn through a paper filter which is also heated, and any traces of particles from the surface of the handbag xe2x80x9cAxe2x80x9d which are picked up on the paper xe2x80x9cBxe2x80x9d will be drawn into the spectrometer 1. If the spectrometer detects the presence of potential contraband, such as, for example, RDX, TNT (trinitrotoluene), or PETN (pentaerythritol trinitrate), then the security officer will typically rerun the test. A second positive result may result in a manual search of the handbag. Given the delays in rerunning samples, as well as the inherent low resolution, it is desirable to have an ion mobility spectrometer which provides more certainty as to the accuracy of the results. Therefore, it is desirable to have an ion mobility spectrometer and ion mobility spectrometry methods which produce precise, accurate results.
Method and apparatus for improved detection and identification of components within a sample using spectrometry are disclosed.
In one aspect of the invention, a spectrometer comprises a sample inlet system configured to introduce a sample into a carrier fluid stream for transport of the sample within the spectrometer as a sample stream. A spectrometry analyzer is positioned downstream of the inlet system and is in fluid communication with the sample stream. The spectrometry analyzer produces signals in response to the chemical composition of components in the sample stream. A flow path is formed between the sample inlet system and the spectrometry analyzer. The spectrometer further comprises a signal processor configured to process the signals produced by the spectrometry analyzer to produce an outlet signal indicative of the presence of an identified substance. The spectrometer further comprises a reagent system configured to selectively introduce at least two reagents into the sample flow path. The reagent system comprises a first reagent reservoir and a second reagent reservoir in selective fluid communication with the sample flow path.
In another aspect of the invention, an ion mobility spectrometer analyte detection and identification verification system is disclosed. The system comprises a first reagent reservoir and a second reagent reservoir. The system further includes a carrier fluid inlet manifold having a sample inlet configured to receive the sample into the inlet manifold, a carrier fluid inlet connectable to a source of carrier fluid, and first and second carrier fluid outlets in respective fluid communication with the first and second reagent reservoirs. Additionally the system comprises an outlet manifold having first and second sample stream inlets in respective fluid communication with the first and second reagent reservoirs, and a sample stream outlet.
In yet another method, the invention encompasses a method for verifying the probable presence of a specific component in a sample. The method comprises the steps of providing a sample to be analyzed for the possible presence of a specific component, and providing a plurality of reactants known to form adducts with the specific component, the adducts having known ion mobilities. The method further comprises the steps of vaporizing and ionizing at least a part of the sample along with at least some of the reactants to create at least one vaporized, ionized analyte stream and then analyzing the analyte stream to determine the existence of components having the known ion mobilities. The existence of components having the known ion mobilities are indicative of the presence of the specific component.